Institute of Electrical and Electronics Engineers (IEEE) 802.11 is a set of air interface specifications in wireless local area network developed for Dedicated Short Range Communication (DSRC) by IEEE Committee, which provides wireless network service based on a competition scheme. In IEEE 802.11 wireless network, before transmitting a data packet, a station (STA) or an access point (AP) needs to monitor a channel to determine whether the channel is clear, and if yes, experience a random back-off process. Or else, the STA or AP cannot transmit the data packet and needs to monitor the channel again. The above monitoring scheme is called clear channel assessment (CCA) which is widely used by STAs or APs in IEEE 802.11.
CCA is a physical carrier sense scheme detecting whether a signal exists in a channel through various means. When a signal is transmitted in the channel and the signal has a relatively high power intensity which may affect data transmission of a STA or an AP, the CCA may indicate the channel as in a busy state and enable the STA or AP to restrain the data transmission. When no signal is transmitted in the channel or signals in the channel have relatively low power intensity which may not affect the data transmission of the STA or an AP, the CCA may indicate the channel as in a clear state and enable the STA or AP to obtain an opportunity of accessing the channel and to enter a state of data transmission.
CCA detects signals, which can be realized by various signal detection methods, and estimates the channel state based on the detected signals. A common method is to use the power of a received signal to determine the channel state. For example, the power of the signal received by the STA or AP may be compared with a CCA threshold which is a fixed value determined according to the IEEE 802.11 specifications. If the power of the signal received by the STA or AP is higher than the CCA threshold, it is determined that the channel has a signal and the channel is indicated to be busy; or else, the channel is indicated to be clear.
When the channel has a high noisy level or when the channel is in a quite busy state, i.e., there are plenty of STAs or APs in the wireless communication network and communications are frequent there, if a STA or an AP needs to send data, it may compete with other STAs or APs. In existing techniques, the CCA threshold is a fixed value. Sometimes, when the STAs or APs are located in communication environment with high noisy level, they can hardly obtain an opportunity to access the channel for a long time, which may cause a throughput rate to be low for a long time or even cause a zero throughput rate, thereby, sometimes, an interruption of communication may occur.